This invention relates generally to atomizing nozzles, and more particularly, is directed to a coating assembly including a plurality of atomizing nozzles.
In the pharmaceutical industry, the use of fluidized bed coaters for coating pharmaceutical materials is well known. For example, it is well known to coat potassium chloride crystals with a polymer in the manufacture of a drug sold under the trademark "K-DUR" by Schering-Plough Corporatoin of Madison, N.J. The coated potassium choride crystals are then formed into tablet form. In such case, the coating ensures that the tablet will dissolve slowly in the stomach and intestines of a user, generally in six to eight hours. It is also known, for example, to coat various drugs, such as the asthma drug sold under the trademark "THEO-DUR" with such a polymer coating.
In this regard, in known fluidized bed coaters, the particles to be coated are suspended in an apparatus that creates a strong upward air current or stream in which the particles move. The stream intersects a zone of finely atomized coating liquid which causes the particles to be coated. Thereafter, the coated particles are dried. The foregoing method and appartus are known, for example, from U.S. Pat. Nos. 3,089,824; 3,117,027; 3,196,827; 3,241,520; and 3,253,944, the entire disclosures of which are incorporated herein by reference.
In addition, such an apparatus is sold by Glatt Air Technique, Inc. of Ramsey, N.J. under Model Number GPCG 300/WURSTER 46". In this particular Glatt apparatus, there are seven atomizing nozzles extending into the coating chamber. Each atomizing nozzle is formed by an elongated hollow air tube, along with a coating supply tube extending through the air tube. The coating liquid is supplied to the atomizing end of the nozzle through the coating supply tube, while the air for atomizing the coating liquid is supplied to the atomizing end of the nozzle through an annular gap formed between the coating supply tube and the air tube. As a result of such air and liquid flow, at the outlets of the air tube and coating supply tube, the air tears the liquid stream into tiny droplets. Accordingly, the coating solution is formed into fine droplets.
However, with such apparatus, the inner diameter of each coating supply tube is substantially equal to the inner diameter of the coating liquid supply line connected therewith. As a result, there is no pressure drop in the coating supply tube, and therefore, no regulation of the flow of coating liquid in the coating supply tube. Therefore, to ensure that the liquid coating solution supplied to the atomizing end of each atomizing nozzle is the same, each atomizing nozzle is provided with its own metering device in the form of a metering pump or a flow meter. Thus, for example, with the Glatt fluidized bed coater, seven metering pumps or flow meters must be provided, one for each atomizing nozzle. Such equipment, however, is costly and requires maintenance and recalibration.
Further, with such known atomizing nozzles, there is a problem of assuring positive separation of the liquid stream from the atomizing air stream inside the nozzle body without the use of O-rings or other sealing devices. This is essential since even a small seepage of air into the liquid stream will cause a malfunction of the atomizing nozzle. For example, the Glatt atomizing nozzles are provided with O-rings which must be taken out to clean the nozzles, and which provide a problem of air mixing with the liquid.